Electric lamp



Dec. 26, 1939.

w. ELENBAAS ET AL ELECTRIC LAMP I Filed April 15, 1938 Inventors:

Willem Elenbaas, Eduard G. .Dorgelo,

Hendricus J. Lenwmens,

Thei Attorneg.

' Patented Dec. 26, 1939' ELECTRIC LAMP Willem Elenbaas, Eduard G. Dorgelo, and Hendricus J. Lemmens, Eindhoven, Netherlands, assignors to General Electric Company, a corporation of New York Application April 15, 1938, Serial No. 202,312

In Germany April 19, 1937 1 Claim.

Our invention relates to electric lamps generally and more particularly to incandescent'electric lamps containing a gaseous atmosphere.

' Still more particularly, my invention relates to 5 electric incandescent lamps containing a vaporizable metal which is vaporized during operation of the lamp. a

It is well known in the lamp art that a particularly efficient incandescent lamp is obtained when the filament burns in a medium of mercury vapor mixed with a rare gas and/or an inert gas with an internal gas pressure above one atmosphere. The pressure ordinarily employed in lamps of this type is generally much higher than one atmosphere, and may be increased to as high as forty or fifty atmospheres.

Mercury vapor has some very important advantages as a medium in which a filament is made to glow. Because of its high molecular weight it has a particularly low thermal conductivity, so that the heat losses to the surroundings in which the lamp operates are relatively small. Likewise, because of its high molecular weight, mercury vapor counteracts or retards to a very great degree the evaporation of the material of which the filament is made. Consequently, the blackening of the glass lamp bulb is relatively slight even after a prolonged period of lamp operation.

The high pressure employed in lamps of the previously mentioned type permits the use of a lamp bulb having a volume of exceedingly small dimensions. The high lamp pressures are obtained in such a way that a quantity of mercury present in the liquid state in the lamp bulb is vaporized by the heat radiated by the filament.

In the operation of high pressure mercury vapor lamps of the aforementioned type it has been found that, in spiteof the use of getters or the like, the lamp bulb, after the lamp has been in operation for a certain length of time, nevertheless becomes blackened as a result of the evaporated filament material. The result is that the amount of power normallydissipated through the glass lamp bulb in the form of light or heat is thereafter reduced. Thus, a part of the power which is normally dissipated through the lamp bulb in the case of a new lamp, (i. e., one in which no blackening or practically no blackening has occurred), is retained in the bulb after the lamp has been in operation some time'and'becomes noticeable by vaporizing a larger amount of the mercury quantity present in the lamp. The effect of this increased mercury vaporization is to increase the internal pressure within the glass lamp bulb abovethe pressure normally existing therein when the lamp is new and the bulb has not yet been blackened. Such increased pressures within the lamp bulb are objectionable because of the danger of explosions. 5 I It has been found that when, in a new lamp operating at the normal operating voltage, at least two-thirds of the quantity of mercury within the lamp is'vaporized, there is then no need to fear that the later occurring higher internal 0 pressures within the bulb, after the lamp has been in operation for some time, will lead to objectionable phenomena, such as explosions. As previously stated, these pressures may be of an order of magnitude of as high as fifty atmospheres. When the quantity of mercury is proportioned inthe above indicated manner, definite assurance is given that the internal operating pressure, after the blackening of the lamp bulb, will never become more than one and one- 20 half times the original operating pressure in the new bulb, and this limit is allowable, as has been shown by tests. Accordingly, one object of our invention is to provide a metallic vapor incan-' descent lamp in which the quantity of the vag5 porizable metal in the lamp bulb is such that the internal pressure within the lamp bulb is maintained within allowable limits, so as to thereby eliminate the danger of explosions.

Another object of ourinvention is to provide a metallic vapor incandescent lamp in which the quantity of the vaporizable metal in the lamp bulb is such that, when the lamp is new and the bulb as yet unblackened, at least two-thirds of the said metal is'converted into the vapor state at the nominal operating voltage applicable to the lamp, 1. e., less than onethird of the mercury remains in liquid form.

Still another object of our invention" is to provide a metallic vapor incandescent lamp in which the quantity of the vaporizable metal inthe lamp bulb is such that, when the lamp is new and the bulb as yet unblackened, the metal will be completely evaporated at a temperature which is at least approximately 10 C. lessthan the ordinary temperature of the lamp at the coolest point.

Further objects and advantages of our invention will appear from the following description of species thereof and from the accompanying drawing which is a longitudinal sectional view, on an enlarged scale, of a metallic vapor incandescent lamp comprising our invention.

Referring to the drawing, the lamp there shown comprises a tubular bulb or envelope I of vitreous material, a pair of current supply or ead wires 2,

3 hermetically sealed in opposite ends of said envelope, and an incandescent body or filament 4 disposed longitudinally in the lamp bulb I and secured at opposite ends to the said current supply wires 2, 3. The bulb l is' preferably made of quartz or other hard glass in order to. withstand the high pressures and high temperatures to which the bulb is subjected during operation of the lamp. The bulb I is adapted to be evacuated and filled with a suitable gas or gaseous mixture through an exhaust tube sealed to the bulb wall, which tube, after exhaustion and filling of the bulb, is fused off to form the exhaust tube tip 5. The lamp bulb contains a filling of a fixed gas,

such as a, rare gas and/or an inert gas, the said filling preferably consisting of a mixture of a certain quantity of argon with nitrogen. In addition, the lamp bulb contains a small but accurately measured quantity of vaporizable metal 6, preferably mercury. This quantity of mercury 6 is such that, when the lamp is new and the bulb as ,yet unblackened, at least two-thirds thereof will be vaporized by the heat radiated by the filament l during operation of the lamp at its nominal operating voltage.

A lamp of the above type has a light intensity of approximately 2200 lumens. Measurements have shown that the 'eficiency of such a. lamp is about 22 lumens per watt.

When a lamp according to our invention is not 1 in operation and is cold, the filament 4 is located in a medium consisting of. a rare gas and/or an inert gas, the preferred medium consisting of a starting curre'nt gradually. The quantity of mercury 6 is then gradually vaporized by the heat radiated by the burning filament 4, so that the same changes into the vapor state and forms, together with the argon-nitrogen mixture in the lamp bulb, a medium which the filament bulb during the life of the lamp therefore eliminstant, a condition of equilibrium is reached in v the lamp at which a certain proportion of the power supplied to the filament 4 will maintain the mercury in the vaporized state. As a consequence of the dimensioning of the mercury quantity 6 so that when the lamp is new and the bulb as yet unblackened at least two-thirds of the mercury is vaporized by the heat'radiated by the filament 4, definite assurance is thereby given that the internal pressure within the lamp bulb will be kept within an upper limit of one and onehalf times the original pressure. Such a definite limitation of the internal pressure in the lamp inates the danger of explosions.

In a preferred construction of the lamp according to the invention, the quantity of mercury 6 present in the lamp, when new, is made such' that it will be completely vaporized at a temperature which is at least approximately 10 C. less than the ordinary temperature of the lamp at the coolest point. In this case the filament 4 will burn, at the ordinary operating temperature, in a medium of unsaturated mercury vapor. As a not detrimentally affected by possible temperature fluctuations to which the outside wall of the lamp bulb may be subjected.

What we'clalm as new and desire to secure by Letters Patent of the United States is:

-An electric incandescent lamp adapted to operate with an internal pressure considerably in excess of one atmosphere and comprising an envelope, a metallic filament sealed within said envelope, a filling of a fixed gas in said envelope which is inert with respect to the material of said filament and serves to prevent excessive evapora tion of said filament during the initial moments of operation of the lamp, said envelope also containing a predetermined quantity of mercury. such that at the nominal. operating voltage of the lamp when new a portion of the said mercury less than one-third of the total amount thefiof is present in the envelope in liquid form.

WILLEM ELENBAAS. EDUARD G. DORGELO. HENDRICUS J. LEMMENS. 

